Short-base range finder



H. D. TAYLOR.

SHORT BASE RANGE FINDER. lAPmcAnoN FILEDl APR. 28.1919.

2 SHEETS-SHEET l.

Patented J une 27, 1922.

H., D.. TAYLOR.

SHORT BASE RANGE FINDER. APPLICATION FILED APR. 2a, .Ia-I9.

2 SHEETS-SHEET 2.

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UNITE@ STATES rarest erstes.4

HAROLD DENNIS TAYLOR, OF BISHOPSI-IILL, ENGLAND, ASSIGNOR 0F ONE-HALF TO ALFRED TAYLOR, OF BISHOPSI-IILL, YORK, ENGLAND.

SHORT-BASE RANGE FINDER.

Specification of Letters Patent.

Patented June 27, 1922.

Application filed April 28, 1919. Serial No. 293,289.

(GRANTED UNDER THE PROVISIONS 0F THE ACT 0F MARCH 3, 1921, 41 STAT. L., 1313.)

T 0 all whom it may concern:

Be it known that I, HAROLD DENNIS TAYLOR, subject of the King of Great Britain. residing at Bishopshill, in the county of York and Kingdom of England, have in vented certain new and useful Improvements in and Relating to Short-Base Range Finders (for which I have filed an application in England April 18, 1918, Patent No.l 125.,- 725), of which the following is a specilication.

The present invention relates to improvements in home base range finders of the type in which two optical squares7 one at each end of a tube reflect a. view of the distant target towards the middle of the tube into a single or double observing telescope.

The invention however will not be generally applicable to range finders where the two end optical squares both reflect off in the same direction, the one over or under the other, into one telescope, because in this case the simple operation of the halving adjustment means always secures that the main axes of the two optical squares are parallel.

l nder certain conditions it is possible for the optical squares of range finders to be mal-adjusted or become maladjusted with resultant errors in the determining of a range of a remote object by the instrument without the observer becoming aware of the fact.

Accordingly by the present invention there is provided, preferably adjacent to the normal viewing eyepiece of the instrument.y the eyepiece of a collimating telescope in the optical system of which telescope is situated a collimating line, which can be viewed by the eyepiece directly and indirectly by reflection in small mirror on the optical square so that any tilting of the optical square will be immediately apparent by a lack of coincidence of the two images of the said collimating line, or a movement of one line relatively to the other as the case may be. f v

lith such. short base range finders it can be shown that as long as the main axis of the optical squares are' upright or perpendicular to the plane of the range triangle, that is the plane containing the base or the longi-y tudinalaxis of the instrument and the distant obJect so long` do they reflect the reflected ray at the minimum angle with the enter ing ray this minimum angle being usually arranged to be approximately a right angle. By the main axis of an optical square is here meant the straight line formed by the intersection of the two reflecting mirrors or planes or any straight line parallel to the same. Further the longitudinal axis of' an optical square is the straight line which, in plan, bisects the angle (of 45) between the two mirrors and lies in the plane of reflec tion or the plane of the range triangle, or any straight line parallel to the optical squares longitudinal axis.

In practice the main axes of the optical squares are set upright in a finished range finder by rocking each optical square about its longitudinal axis by 10 minutes of arc in either direction and seeing that it gives equal range readings when in either extreme position andV adjusting it todo so. There are also two other axes of an optical square to be considered, one being the first secondary axis pointing to the distant target and the other or second secondary axis is the axis of the main tube along which the rays reliected from the target pass to the central telescope or telescopes.

It can be shown that if the right hand optical. square becomes tilted or rotates about its first secondary axis,v awa-y fromits trulyV upright position, then the object as seen in the erecting telescope will move to the left slightly in accordance with the following table.

Angle of tilt about rst secondary axis.

Deviation of image to left.

place, then after both optical squares have tilted away from one another, 'for example by 7-.1 minutes ot arc for each optical square, then the two images willbecome separated by 2 seconds of are and a wrong range read# ing will be registered: supposing that no means be provided for restoring both optical squares to verticality.

`lt can be shown that ifthe halving line oi a range finder be made to bisect inthe held of view7 a certain point on a distant upright mast and thenthe two opticalfsquares become equally tilted `about their first secondary aires, the upper ends of their' main axes both leaning away 'from the centre ol. the instrument,. then both the images will drop by equal amounts in the field of view so that il. there was i vertical coinci dence or freedom from halving error when the optical squares were upright, there will still be vert-ical coincidence or freedom 'from halving error after the equal tiltings of the optical squares have taken place, therefore the observer is left with no indication whatever oi the fact that the optical squares have gone out of upright, so that liis range readings may bemore or less vitiated without his suspecting any error;

This actually may' take place when warm sunshine is allowed to ,tall on the top of the range` finder7 causing` the "top half ot the tube toiexpand relatively to thev lower halt.y which naturally causes the two optical squares to tilt away romxone another and by an angular amount which may be expected tovary with the length of the instrument, sothat doubling the latter, should lbe expected to quadruple the optical errors and so on,

` Not only are the main tubes liable to buckle because heated unequally on top and bottom sides.,` but in many cases they buckle or deviate" from straightness under changes of temperature quite apart trom unequal heating. A tube may beperitectly straight at a uniform temperature of T5 degrees and yet buckleat 35 degrees. y y

It is the object of rny invention to enable the observer to keep a. check upon the uprightness of the two optical squares by means of a very simple observation and adjustment, which latter works in with the adjustment for halving error that is always provided with a range finder.

The invention is more particularly described with reiterence tothe accompanying drawingdiagrammatically showing` Aone arrangement by way of example, and in i Fig.` :l i is .af diagrammatic `view of" part of c a: range lindert Y. j Frg. laf 1s a "side vieuroil the roof prism ot Fig. 3 is a 'corresponding vertical longitudinal section.

Figures 4 and 5 are details showing,` the mountingof the mirror.

Fig; t3 shows the collimatingsystem in relation to a range finder. i At a place conveniently close-by the cyepiece 18 of the observer or range-taker the eyepiece 1 oi a small seli colliinatingI telescope is mountedy which, a little way inside the main tube is elbowed and has a reiiecting prism, preferably an erecting or iooiprism 2 mounted in the elbow and reflecting oil' in a direction towards the right hand optical square 19 in the arrangement shown,y and parallel to the base line of therange iinder` A small telescope objective 3 carriel'l either by a tube or bracket is mounted at its principal iocal distance trom the eyepiece 'focal planea so that the whole 'forms an elbow/ad,

telescope (whose magnir'ying` power should bc about l() to 11.5 diameters) directed towards a part of the frame work of one or the other of: the two optical squares 119, 2() (or in ce1.'-

tain cases each alternately iii'desired) and to.

this latter frame work a silveredI plane mirror 4, Figures 4t and 57 oit upright rectangir lar forni (say about 2 to El high by 1 wide) is fixed with three adjustable 5, 6,. l' bearings so that it can be fixed in a plane perpendicular to the projectedv line oi1 collimation of the said elbowed telescope.

.l n the iloca'l plane of the collimating telescope is placed a diaphragm 8, Figs. l and 3 of plane unsilvered (generally d50) with thcfoptic axis and this has a horizontal silyered line 9g see Fig.. 2 on it oit about inch width stretching' across from one edge to the centre of the diaphragm and continuous withA its centre is an opaqueblack lino lOabout O05 width drawny across the other half of the diaphragm. The silvered line is arranged to be on the eyepiece side ol'jthe glassl so as to re# Heet as a bright line towards the objective by internal reflection. i

Somewhere just above the;` diaphragm is placed a disc or window 1l F ig. 3 ot ground or opal glass illuminatedeither by the sky or by a small electric lanip; This supplies a back-ground of light'for the illumination ot the diaphragm 8. V

Let it be supposed that the `telescope is vtinted, to look towards the right, hand optical square framee which carries the adjustable mirror asshown. Inthe course oft adjust ment oit' the range finder the main axis of this optical square is iii-st set truly` upright by the usual tilting` about its y' longitudinal axis as previously described. This having been done;` then the mirror t must be care;

glass placed at an angle,

fully adjusted so asto reflect the pencilof T parallel rays received from the centreI point of the telescope diaphragm and emerging from the object glass back again on the said course or axis so as to be refracted back again by the objective and come to focus at the centre of the diaphragm. As a result of this then an image of the luminous silvered line will be formed uponv the black line which latter will appear to bisect it longitudinally. t'the same timevtlie whole field will be lled with La semi-luminous back ground of light reflected from the unsilvered surfaces of the diaphragm.

If now anything causes the right hand half of the main tube of the range finder to buckle in a vertical plane, such as hot sunshine on the top then the main axis of the right hand optical square will become tilted away from the telescope, that is the optical square will rotate about its first secondary axis (or the line pointing to the distant target) and the attached mirror 4 will now reflect the return beam upwards, consequently the return image of the silvered line as seen in the erecting telescope will be seen to drop down in the field of view of the collimating telescope as at 12 (Figure 2).

As described in specification No, 1013849, the optical square may be tilted about an axis pointing towards the distant target by turning a milled head or the like conveniently near the eye-piece.

If this milled head be now operated then the optical square is tilted back again until the image of the silvered line is again projected upon the black linel` when it is clear that the optical square has been restored to perfect uprightness.

If now the other or left hand optical square is also out of upright the effect seen in the field of view of the range finder proper will be a very perceptible havling error. the image from the left hand optical square in this case will be projected lower down in the field than that from the already adjusted right hand one, and all that is necessary to restore the left hand optical square tov uprightness is to tilt it about its first secondary axis until the halving error disappears, when its main axis must of necessity' be again upright. This is of course done by turning round another milled head which causes the left hand optical square to tilt about an axis placed parallel to its first secondary axis, as in the case of the right hand one. Y

In this way the uprightness of the two optical squares may be kept easily within two minutes of error. Of course other forms of markings may be adopted for the diaphragm of the collimating telescope but I have described what seems to me to be the simplest and best form.

It will easily be surmised that the optical squares are notI likely to become tilted about their secondary axis or the axis of the main.- tube, forj it- 'would require van I lexceedingly improbabletorsion vor spiral twist of the tube to bring that about.`

So that when using a range finder for-ac# tually taking range readings', the observer can if need be7V first glance into the eyepiece of the collimating telescoperandby means of the right hand halving error adjuster milled head restore the right hand optical square-to u-prightness.v I-Ie then'looks into the range finder eyepiece at the distant target and eliminates any noticeable halving error by operating the left hand halving error adjuster milled head after which coincidence observations for range taking may fitly be undertaken.

It is important that the field of view of this collimating telescope should be fairly large and also that the free distance between the eye and the lenses should be as large as possible and therefore I recommend a form of eyepiece which formed the subject of my British patent application No. 9565/1918., consisting of a triple cemented aehromatic lens 14 and a double cemented achromatie lens 15.

The method of fixing the mirror 4 in Figures 4 and 5 is substantially described in British patent specification 7892 of 1910 and consists in holding the mirror between flat metal pallets 16 which have free ball and socket bearings on the ends of the screws 5, 6 and 7 which are fixed adjustably through the frame, and corresponding pallets on the other side pressed onto the glass by means of the springs 17 armed with points pressing into small recesses in theV pallets. The pairs of pallets being opposite to one another and free to bed themselves do not exert. any distorting effects on the mirror, although holding it immovable.

I declare that what I claim is z- 1. A device for testing the adjustment of opticalV squares of range finders comprising in combination a collimating telescope system, a collimating mark, and a small plane reflecting mirror mounted on the framework of the said optical squares.

2. A device for testing the adjustment of optical squares of range finders comprising in combination a collimating telescope, a reflector mounted on one of said optical squares, and a plane glass diaphragm placed obliquely in the focal plane of said telei scope having a horizontal mark extending from one edgey to the centre of said diaphragm.

3. A device for testing theadjustment of opt-ical squares of range finders comprising a collimating telescope, a reflector mounted on one of said optical squares and a plane glass diaphragm placed obliquely in the focal plane of said telescope having a hori- Y zontal mark extending from one edge to the reading marks in alignment each extending across half of said diaphragm.

In Witness whereof, I have hereunto signed my name this 9th day of April 1919, in the presence of two subscribing Witnesses. 15

HAROLD DENNIS TAYLOR.

fitnesses GEORGE WILLIAM CURRY, DOROTHY ADELAIDE IIAZELL. 

